1) Field of the Invention
The present invention relates to a cleaning unit that cleans toner on an image carrier, a process cartridge that employs the cleaning unit, an image forming apparatus, and toner.
2) Description of the Related Art
A color image forming apparatus that employs an electrophotographic system is now widely used. Moreover, a high-definition of an image to be printed is desired in association with easy availability of digitalized images. In the study of higher resolution and gradation of images, further conglobation and granulation to finer particle diameter are under research for improvement of a toner that makes latent images visualized in order to form images with the high definition.
For example, several methods are proposed, in which conglobated ground-type toner having a specific particle diameter distribution is obtained (see, for example, Japanese Patent Application Laid-Open Publication No. 1989-112253, Japanese Patent Application Laid-Open Publication No. 1990-284158, Japanese Patent Application Laid-Open Publication No. 1991-181952, and Japanese Patent Application Laid-Open Publication No. 1992-162048), toner conglobated and granulated to smaller particle diameter by suspension polymerization is obtained (see, for example, Japanese Patent Application Laid-Open Publication No. 1993-72808), toner conglobated and granulated to finer particle diameter is obtained by mixing a binding resin and a colorant in a solvent that is not mixable with water, followed by dispersing the mixture in an aqueous solvent in the presence of a dispersion stabilizer (see, for example, Japanese Patent Application Laid-Open Publication No. 1997-15902), and toner conglobated and granulated to smaller particle diameter is obtained by mixing a binding resin containing a partially denatured resin and a colorant in an organic solvent and dispersing the mixture in an aqueous solvent, followed by polyaddition reaction of the denatured resin (see, for example, Japanese Patent Application Laid-Open Publication No. 1999-133668). With the use of the above type of toner, image quality and fluidity are improved.
The toner granulated to finer particle diameter and conglobated is suitable for obtaining images with the high definition because the toner is accurately transferred; however, the conglobated toner is easy to roll down. Therefore, the toner rolls between a cleaning blade and a photosensitive member in a cleaning unit, which makes cleaning difficult. This may result in causes of abnormal images such as background fog.
Accordingly, an electrophotographic image forming method, for example, is proposed. In the electrophotographic image forming method including a cleaning member that cleans, with an elastic rubber blade, residual toner on the photosensitive member after toner has been transferred to a recording material, the toner contains zinc stearate of not less than 0.01% and not more than 0.5% with respect to the toner weight, and the elastic rubber blade is essentially retained, on the side of the cleaning blade abutting on the photosensitive member, to a supporting member to fix the blade to the cleaning member (see, for example, Japanese Patent Application Laid-Open Publication No. 1999-184340). However, there is a disadvantage that when zinc stearate is added to the toner, the zinc stearate on the photosensitive member becomes nonuniform depending on conditions of images to be developed.
In addition, a cleaning unit provided with a brush-shaped roller that is arranged with abutment on an electrophtographic photosensitive member drum on more upstream side of rotational direction of the electrophotographic photosensitive member drum compared to the cleaning blade is proposed (see, for example, Japanese Patent Application Laid-Open Publication No. 2003-140518). In this cleaning unit, applying a lubricant over the photosensitive member with a conductive brush is disclosed. However, there is a disadvantage that the lubricant and toner adhere to the surface of the brush, which are hard to remove, resulting in decrease in applying performance of the lubricant.